With the development of an audio signal coding/decoding technology, more and more electronic equipments transmitting data via an audio interface are produced. For example, the electronic equipment may be connected with a mobile communication device (such as a mobile phone) via a loudspeaker interface (such as a headphone interface) of the mobile communication device for receiving an audio signal output from the mobile communication device, and can also receive the audio signal output from a loudspeaker of the mobile communication device or a loudspeaker of a fixed telephone device via a microphone (MIC).
Furthermore, with the popularization of a USB interface, a large number of electronic equipments are provided with the USB interface. Thus, how to receive the audio signal output from the loudspeaker of the mobile communication device or the loudspeaker of the fixed telephone device via the USB interface of the electronic equipment is a technical problem which needs to be solved currently.